Conventionally, tacky adhesion sheets have been used for surface protection and damage prevention of the products when optical parts such as lenses, and semiconductor products such as semiconductor wafers are subjected to high-precision processing in optical industry, semiconductor industry, and the like. For example, in production steps of semiconductor chips, the semiconductor chip is produced by: slicing highly purified silicon single crystals or the like to give a wafer; incorporating an integrated circuit by etching of a certain circuit pattern such as IC on the wafer surface; grinding the back face of the resulting semiconductor wafer by way of a grinder to reduce the thickness of the semiconductor wafer to about 100 to 600 μm; and dice cutting the semiconductor wafer following grinding to a predetermined thickness, thereby forming a chip.
According to the production of the semiconductor chip described above, the semiconductor wafer itself has a small thickness, and is fragile. In addition, because of the relief structure of the circuit pattern, the wafer is liable to be damaged when external force is applied during carrying to the grinding step or the dice cutting step. Additionally, in order to remove the polishing dust generated in the polish processing step, or to eliminate the heat generated during polishing, the grinding process is carried out while washing the back face of the semiconductor wafer with purified water. Therefore, it is necessary to prevent the circuit pattern face from being contaminated by the rinse water and the like yielded in the washing. Accordingly, in order to protect the circuit pattern face of the semiconductor wafer, and concurrently to prevent damage of the semiconductor wafer, the grinding operation has been carried out with a tacky adhesion sheet for processing attached onto the circuit pattern face. Moreover, in the dice cutting, a protective sheet is attached on the back face side of the wafer, and the dice cutting is conducted in a state with the wafer being adhered and fixed. The thus obtained chip is picked up by sticking from the film substrate side with a needle, and then fixed on a die pad.
Known exemplary tacky adhesion sheets for high-precision processing include, e.g., those having an adhesive layer formed from an adhesive composition provided on a substrate sheet of polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), an ethylene-vinyl acetate copolymer (EVA) or the like (for example, Patent Document 1, Patent Document 2, Patent Document 3).
Furthermore, a constitution in which a protective substrate produced by impregnating a ladder type silicone oligomer into an aluminum nitride-boron nitride sintered compact with pore is used in place of the protective tape, and this protective substrate is adhered to a semiconductor wafer using a thermoplastic film is also disclosed (Patent Document 4). In addition, a constitution in which a material such as alumina, aluminum nitride, boron nitride or silicon carbide having substantially the same coefficient of thermal expansion as that of the semiconductor wafer is used as a protective substrate and using a thermoplastic resin such as polyimide as an adhesive for adhering the protective substrate with the semiconductor wafer, a film having a thickness of 10 to 100 μm is provided by applying this adhesive composition, and a method which includes spin coating of an adhesive composition, and drying to give a film having a thickness of no greater than 20 μm were proposed (Patent Document 5).
Furthermore, in recent years, as multilayer-wiring of semiconductor elements has progressed, a process in which: a protective substrate is adhered using an adhesive composition on the surface of a semiconductor wafer having a circuit formed thereon; the back face of the semiconductor wafer is polished; thereafter, the polished face is etched to give a mirror face; and a circuit on the back face side is formed on this mirror face has put into practice. In this case, the protective substrate is kept adhered until the circuit on the back face side is formed (Patent Document 6).
Patent Document 1: Japanese Unexamined Patent Application, First Publication No. 2003-173993;
Patent Document 2: Japanese Unexamined Patent Application, First Publication No. 2001-279208;
Patent Document 3: Japanese Unexamined Patent Application, First Publication No. 2003-292931;
Patent Document 4: Japanese Unexamined Patent Application, First Publication No. 2002-203821;
Patent Document 5: Japanese Unexamined Patent Application, First Publication No. 2001-77304;
Patent Document 6: Japanese Unexamined Patent Application, First Publication No. S61-158145;